Put the potatoes in a saucepan of cold salted water (dissolve the salt completely to preserve the stainless steel surface).
Cook them for 25 minutes.
Drain and peel the potatoes. Mash half the potatoes with a fork.
Leave the mash to cool, then add the wheat and buckwheat flours.
Next add the eggs, the milk and the cream.
Melt a small knob of butter in each blini pan on a moderate heat.
Ladle a small quantity of batter into each pan.
Cook the blinis for two minutes on each side.
Cut the smoked haddock into thin strips.
Finely dice the remaining potatoes and the strips of smoked haddock.
Combine the crème fraîche, the mustard, and the chopped dill.
Mix all the ingredients together.
Garnish the warm blinis with the topping and serve immediately.